Organic semiconductors, including image sensor circuits, have many potential advantages over traditional amorphous silicon-based semiconductors. The chemicals used in the photodiode for the image sensor circuit can be tailored to be sensitive to different frequencies ranging from ultraviolet to infrared. The chemical films have lower stress and lower process temperatures; thus, working well with lower temperature applications, such as flexible substrates.
Manufacturing of individual organic photodiodes on a substrate to create photo sensing arrays remains a challenge. The thin film transistor (“TFT”) backplane upon which the organic photodiode is deposited must be free of any organic or inorganic residue, such as residual photoresist, etch process compounds and must be very planar. This is especially important when making a photo sensitive array. If the surface is not free of any residue, then the organic chemical will not have sufficient electrical contact with the bottom electrode of the TFT backplane. This will cause non-repeatable performance from the photo sensing array from one process run to another. If the TFT backplane electrode is not planar, then the organic material may not completely cover the electrode and possible electrical shorts will result. Even if the organic material is able to cover the uneven electrode surface, performance of the organic material will be inconsistent and unrepeatable.
What is desired is an improved process of cleaning and optimizing the surface of the TFT backplane to ensure repeatable performance of an organic semiconductor.